1. Field
This invention pertains generally to nuclear reactor containment ventilation systems and more particularly to a wet filter for such systems.
2. Related Art
In many jurisdictions, nuclear power plants must be designed to ensure that even in the event of accidents, a mechanism will be provided to prevent or minimize the escape of radioactive material and noble gases. To guard against radioactive releases, the reactor system is typically housed within a primary containment structure that is constructed from steel and reinforced concrete. The primary containment vessel is designed to be capable of withstanding large pressures which may result from various accident scenarios. However, it has been postulated that in severe accidents, the containment vessel itself could fail from gradually increasing pressure. Although the likelihood of such an event is considered very small, the health risks associated with exposing the surrounding population to the radioactive releases of such an event has led many to believe that a mechanism should be provided to filter the gases and minimize the release of radioactivity, if the containment vessel is vented to reduce its pressure. That is, it is desirable to both provide a pressure release device for the containment vessel and a mechanism for filtering any gases that may be released by the containment before they are released into the atmosphere.
The nuclear accidents at Chernobyl, Ukraine in 1986 and more recently Fukushima Dai-ichi in Japan in 2011, clearly show the consequences of a release of fission products with long decay times. Large ground areas surrounding the damaged power plants were contaminated and rendered not suitable for use for several decades. The cost impact is tremendous. Short-lived fission products such as iodine in different forms, while more harmful to people, have consequences that are more easily managed. Fission products in the form of small aerosols, which are long lived, can be spread over large distances, depending on meteorological conditions. As a result of these accidents, the governments of many countries have decided that nuclear power plants must install filtered containment ventilation systems to protect people and the surrounding land from damage due to radioactive contamination.
In the past, a number of filtration systems have been proposed, such as the one described in U.S. Pat. No. 4,610,840, issued to Leach and assigned to the Assignee of this invention. Leach discloses a fission product scrubbing system for a nuclear reactor. Specifically, a second compartment in fluid communication with the containment is partially filled with water. In the event of a large pressure increase, a ruptured disc disposed within a vent pipe emanating from the secondary compartment bursts to relieve pressure. When the rupture disc blows, radioactive gases and vapors from the containment pass through the water filled secondary compartment and are then released through the now open vent pipe. As the hot containment gases and vapors pass through the water stored within the enclosed secondary compartment, a large portion of the fission products will be scrubbed from the containment gases. While such a system can be effective, there is still room for improvement for reducing the size and increasing the effectiveness of such a system to minimize any exposure that such a release may potentially cause.
Accordingly, it is an object of this invention to provide a more effective filter that will minimize, if not completely remove any radioactive effluent that may be entrained in any release of gases from a nuclear primary containment.
It is a further object of this invention to provide such a filtration system that can be supported within a nuclear primary containment or the existing or new buildings near the primary containment without taking up substantial space.